import { BusConnector } from '../bus.js'

interface InBrowserNetworkConfig {
    id?: number
}

/**
 * Network adapter "inbrowser" which connects the emulated NIC
 * to a shared in-browser BroadcastChannel.
 *
 * NOTE: BroadcastChannel.postMessage() sends the given message to
 *       *other* BroadcastChannel objects set up for the same channel.
 *       Since we use the same BroadcastChannel instance for both
 *       sending and receiving we do not receive copies of our
 *       own sent messages.
 *       Source: https://html.spec.whatwg.org/multipage/web-messaging.html#broadcasting-to-other-browsing-contexts
 */
export class InBrowserNetworkAdapter {
    bus: BusConnector
    bus_send_msgid: string
    bus_recv_msgid: string
    channel: BroadcastChannel
    is_open: boolean
    nic_to_hub_fn: (eth_frame: Uint8Array) => void
    hub_to_nic_fn: (ev: MessageEvent) => void

    constructor(bus: BusConnector, config: InBrowserNetworkConfig) {
        const id = config.id || 0

        this.bus = bus
        this.bus_send_msgid = `net${id}-send`
        this.bus_recv_msgid = `net${id}-receive`
        this.channel = new BroadcastChannel(`v86-inbrowser-${id}`)
        this.is_open = true

        // forward ethernet frames from emulated NIC to hub
        this.nic_to_hub_fn = (eth_frame: Uint8Array) => {
            this.channel.postMessage(eth_frame)
        }
        this.bus.register(this.bus_send_msgid, this.nic_to_hub_fn, this)

        // forward ethernet frames from hub to emulated NIC
        this.hub_to_nic_fn = (ev: MessageEvent) => {
            this.bus.send(this.bus_recv_msgid, ev.data)
        }
        this.channel.addEventListener('message', this.hub_to_nic_fn)
    }

    destroy(): void {
        if (this.is_open) {
            this.bus.unregister(this.bus_send_msgid, this.nic_to_hub_fn)
            this.channel.removeEventListener('message', this.hub_to_nic_fn)
            this.channel.close()
            this.is_open = false
        }
    }
}